The present invention relates to automobile headlamps provided with an inclined glass and a generally parabolic reflector.
In general automobile headlamps have a reflector co-operating with at least one light source in order to reflect a beam of essentially parallel rays in the direction of a diffusion glass which can be integral either with the reflector or with the body of the automobile. The glass is provided at least in certain regions with diffusion ribs and/or prisms in order to give a suitable spread to the beam which is finally emitted.
In modern automobile constructions there is a tendency for aesthetic reasons to give the glasses an inclination corresponding to the lines of the vehicle, this inclination generally being from top to bottom and from back to front. Thus very great inclinations of the glass can be achieved, for example of the order of 45.degree. with respect to the vertical. In certain cases, for example for headlamps placed below a grille, the inclination may be in the opposite direction.
In such structures, the inclination of the glass results in a deflection downwards of certain light rays, in particular those which the glass should deflect horizontally. It might be mentioned that for a glass inclined at 45.degree. a ray deflected horizontally by 17.degree. is deflected vertically by 2.5.degree.. This results in illumination which is no longer satisfactory, particularly for the rays which form the dipped beam below the cut-off.
FIGS. 1 and 1a, 2 and 2a illustrate this difficulty.
FIG. 1 shows a conventional headlamp incorporating a parabolic reflector R having a focus F, two filaments for main beam and dipped beam F.sub.R and F.sub.C and a glass closure G. The dipped beam filament F.sub.C is advantageously arranged a little in front of the focus F of the reflector; the main beam filament F.sub.R is slightly displaced towards the rear, encroaching a little on the focus. In the example of FIG. 1 the glass G is vertical. The illumination given by such a headlamp on a standard screen at 25 meters is shown in FIG. 1a. For a central zone of the glass provided with the usual deflecting ribs this gives a band of light the limit of which is horizontal, as shown in FIG. 1a.
If one considers the headlamp of FIG. 2, where the glass G which is analogous to the preceding one and is in this case inclined, the band of light is curved as shown in FIG. 2a. Thus the beam is deflected along its width. This change in the appearance of the beam is not satisfactory since all the light thus lowered impinges upon the road too close to the vehicle and is at least partially situated outside the driver's field of vision. This results in a substantial reduction in driving comfort.
This disadvantage is general but applied more particularly to the formation of the dipped beam for rays situated immediately below the cut-off.